Liquid crystal display apparatuses have been widely used in the art as a screen for a word processor or a computer. Recently, such liquid crystal display apparatuses have rapidly become popular for a screen of a TV.
Most of the liquid crystal display apparatuses adopt a TN (Twisted Nematic) mode. When being obliquely viewed, the liquid crystal display apparatuses have problems of easy reduction of contrast and easy reversal of a gradation characteristic, respectively.
In view of the circumstances, a liquid crystal display apparatus of a VA (Vertically Aligned) mode has recently attract attention. A liquid crystal cell of the liquid crystal display apparatus of the VA mode is configured such that a nematic liquid crystal having a negative dielectric anisotropy property and a vertically aligned layer are combined. Note that a liquid crystal display apparatus having such a configuration is disclosed in FIG. 1 and FIG. 2 of Japanese patent unexamined patent publication No. 2002-202511 or in FIG. 38, FIG. 42, and FIG. 44 of Japanese patent examined patent publication No. 2947350.
When no voltage is supplied, liquid crystal molecules of a liquid crystal cell in the liquid crystal display apparatus align vertically with respect to a surface of a substrate in accordance with control force derived from the vertically aligned layer. In contrast, when a voltage is supplied, the liquid crystal molecules align obliquely in accordance with a magnetic field formed obliquely with respect to the surface of the substrate. This causes the light passing through the liquid crystal cell to have a retardation (a phase contrast) that varies depending on the supplied voltage.
Note that absorption axes of polarization plates provided on both sides of the liquid crystal cell are disposed so as to be orthogonal to each other. The light incident on the polarization plate on an outgoing light side becomes elliptically polarized light that varies depending on a retardation caused by the liquid crystal cell, accordingly. On this account, one part of the incident light passes through the polarization plate. This allows the outgoing light from the polarization plate to be controlled in accordance with the supplied voltage, thereby enabling to carry out the gradation display.
According to the configuration, when no voltage is supplied, since the liquid crystal molecules in the vicinity of the alignment layer are almost vertically aligned, it is possible to bring a marked improvement in contrast and also possible to bring a superiority in viewing angle property.
Meanwhile, a liquid crystal display apparatus, in general, has a slower response speed than a CRT (Cathode-Ray Tube) or other display device. A response sometimes is not completed, because of a gradation transition, within a rewriting period of time (16.7 msec) that corresponds to an ordinary frame frequency (60 Hz).
In view of the circumstances, a method is adopted in which a driving signal is modulated and driven so as to facilitate a transition from a current gradation to a target gradation, thereby improving the response speed. Note that a liquid crystal display apparatus adopting such a method is disclosed in FIG. 4 of Japanese patent examined patent publication No. 2650479.
According to the method, for example, in the case where a gradation transition from a current frame FR(k−1) to a target frame FR(k) is carried out based on a rise driving that causes the gradation to increase, a voltage is supplied to a pixel so as to facilitate the transition from a current gradation to a target gradation. More specifically, a voltage having a higher level than a voltage level indicative of an image data D(I, j, k) of the target frame FR(k) is supplied to a pixel. On the contrary, in the case where a gradation transition from a current frame FR(k−1) to a target frame FR(k) is carried out based on a decay driving that causes the gradation to decrease, a voltage is supplied to a pixel so as to facilitate the transition from a current gradation to a target gradation. More specifically, a voltage having a lower level than a voltage level indicative of an image data D(I, j, k) of the target frame FR(k) is supplied to a pixel.
As a result, when a gradation transition occurs, a brightness level of a pixel changes more rapidly, and reaches, in a shorter period of time, near a brightness level that corresponds to an image data D(I, j, k) of the target frame FR(k), as compared to a brightness level in a case where a voltage level indicative of an image data D(I, j, k) of the target frame FR(k) is supplied from the beginning. This ensures to improve the response speed of the liquid crystal display apparatus even when the response speed of the liquid crystal is slow.
However, in the liquid crystal display apparatus of the vertically aligned mode and the normally black mode, a mere facilitation of the gradation transition like other liquid crystal is likely to occur that the image deteriorates and that the response speed is not fully improved.